The primary goal of this project is to identify and characterize new targets for medication development in the area of pain control and drug abuse. Recent years have seen a resurgence of opioid abuse, as well as the need for additional analgesics with limited abuse potential. Our objectives are to identify new lead drug candidates for further development and to identify and characterize modulatory systems that influence opioid action. The project contains three major aims. The first aim addresses molecular mechanisms of the anti-opioid sigma1 receptor system, looking for additional splice variants of the recently cloned sigma1 receptor and mechanisms through which these proteins modulate the functional aspects of G-protein coupled receptors. By isolating and cloning additional splice variants, it may be possible to identify novel targets for drug development. Sigma1 agonists potently reverse the analgesic activity of a variety of classes of opioid analgesics while sigma1 antagonists potentiate opioid analgesia. The second aim will explore the ability of sigma1 systems to selectively enhance opioid analgesia and not other opioid actions, as well as the role of sigma1 receptors in influencing the expression of ATP-binding cassette (ABC) transporters. The most prominent member of this family, P-glycoprotein (i.e. mdr) has been implicated in the blood-brain barrier, as well as providing a system for transporting endogenous neuropeptides/transmitters from the brain to the peripheral circulation. It also plays a major role in morphine tolerance, with chronic morphine upregulating its expression. In addition to Pgp, MRP1 also has been implicated in opioid action. The last aim involves further studies with a series of opioid analogs synthesized in the laboratory during the previous granting period and the synthesis of a series of new tools to assist in the study of opioid systems. By understanding how opioids and their modulatory systems interact, we hope to develop better approaches towards the management of pain and the discovery of new agents. This proposal explores new potential targets for medication development. Through a better understanding of sigma1 receptors it is hoped to maintain pain control while minimizing side-effects and possibly abuse liability while other aspects of the project explore novel opioid analgesics and antagonists with unique pharmacological profiles.